Intestinal Parasite's Mysteries Revealed

Release Date:
Alisa Zapp Machalek, NIGMS

Giardia lamblia is a major cause of intestinal disease worldwide and the most frequent non-bacterial cause of diarrhea in North America. Nonetheless, the basic biology of this parasite--including how it ravages the digestive tract--is poorly understood.

 Giardia lamblia

Giardia lamblia, a single-celled parasite, causes severe
diarrhea and abdominal cramps.

The organism exists in two different forms--a hardy, dormant cyst that contaminates water or food and an active, disease-causing form that emerges after the parasite is ingested. NIGMS grantee Dr. Frances Gillin of the University of California, San Diego and her colleagues cultivated the entire life cycle of this parasite in the lab and identified biochemical cues in the host's digestive system that trigger Giardia's life cycle transformations. They also uncovered several tricks the parasite uses to evade the defenses of the infected organism. One of Giardia's techniques is to alter the proteins on its surface, which confounds the ability of the infected animal's immune system to detect and combat the parasite. This work reveals why Giardia infections are extremely persistent and prone to recur. In addition, these insights into Giardia's biology and survival techniques may enable scientists to develop better strategies to understand, prevent, and treat Giardia infections.


Hetsko ML, McCaffery JM, Svard SG, Meng TC, Que X, Gillin FD. Cellular and transcriptional changes during excystation of Giardia lamblia in vitro. Exp. Parasitol. 1998;88(3):172-83.

Svard SG, Meng TC, Hetsko ML, McCaffery JM, Gillin FD. Differentiation-driven surface antigen variation in the ancient eukaryote. Molec. Microbiol. 1998;30:979-89.

Reporters may call Alisa Zapp Machalek at (301) 496-7301 to obtain the name of a scientist in the NIGMS Division of Cell Biology and Biophysics who can comment on this work.